Even if it doesn't officially support Firefox 9 now, you can make it work by disabling the addon compatibility check. To disable the addon compatibility check you can install Add-on compatibility reporter ( https://addons.mozilla.org/en-US/firefo ... -reporter/ ) and disable the add-on compatibility check or;

1. Write about:config on your address bar and press enter2. Accept that there are dragons in there3. Right click on that page4. New > Boolean5. Write "extensions.checkCompatibility.9.0a"6. Set it to false7. Restart your browser

After these steps the addon will work flawlessly. I'm currently using SP on a Firefox Nightly Build.